Systems for the collection and analysis of soil solutions for various agricultural and environmental studies have been extensively developed over a number of decades. Soil solutions are generally defined as the interstitial water in the soil, together with solutes and dissolved gases. The literature contains extensive disclosures of devices, sometimes called lysimeters, for the in situ collection of representative soil solution samples. One type, sometimes called a suction lysimeter, consists of a receptacle to be implanted in the earth. An air conduit extends from the earth's surface into the receptacle. By drawing a vacuum on the air conduit, soil solution is drawn in from the surrounding soil through the porous walls and collected in the receptacle. A separate conduit for transferring the soil solution sample brings the sample to the surface when positive air pressure is applied to the receptacle through the air conduit. Alternatively, transfer to the surface may be effected by vacuum if from a relatively shallow sampler, although this is less desirable because of the danger of volatilizing components of the sample. This invention is directed to soil solution samplers of this general type.
The predominant type of suction lysimeter in use is one employing a porous ceramic cup adhered to the bottom of a closed plastic tube, typically by an adhesive. Concern over the accuracy and representativeness of samples collected with this type of sampler has been widely reported. The possibilities of sample contamination with respect to certain component analyses exist with the use of the standard suction lysimeter. Potential contamination includes the introduction of extraneous components to the sample as well as the tendency to remove constituents from the soil solution, and thus distort the analytical results derived from the sample. For example, one concern is the ability of the porous ceramic cup to absorb certain constituents of the soil solution. Contamination may also occur by leaching of anions from the ceramic material. Moreover, adhesives used in assembling the device may contribute contaminants to the sample.
As a result of these concerns, various other materials for the porous medium through which the soil solution will pass into the receptacle have been proposed. Such alternate materials include, for example, fritted glass, alundum, sintered glass, Teflon.RTM. and hollow cellulose fibers. An extensive review of lysimeter types and methodology as described in the technical literature may be found in a recent article entitled "Review of Solution Samplers" by M. Iggy Lataor, published in Water Resources Research. May 1988, Vo. 24, No. 5, pages 727-733.
The concept of this invention encompasses a soil solution sampler which addresses many of the concerns of the art concerning contamination, and which is readily fabricated without the use of adhesives. Samplers may be constructed in accordance with one aspect of the invention so as to be usable in very deep testing locations.
The improved strength of samplers constructed in accordance with the invention is a substantial advantage. Loss through breakage is reduced, particularly in deep soil placements. Installation may be effected in some soils by pressing the sampler into the ground, without the necessity of pre-drilled holes which increase installation cost.